What are net effects of PTH on serum mineral levels?

What are net effects of PTH on serum mineral levels?

• A. Increased serum calcium, decreased serum phosphate.
• B. Decreased calcium, increased phosphate.
• C. Increased both calcium and phosphate.
• D. Decreased both calcium and phosphate.

Answer: (A)

PTH raises serum calcium while lowering serum phosphate. It does this through coordinated actions on bone, kidney, and intestine. In bone, PTH stimulates osteoclast activity, releasing calcium and phosphate into the bloodstream. In the kidney, PTH increases calcium reabsorption in the distal tubule, and promotes phosphate excretion by reducing phosphate reabsorption in the proximal tubule. It also stimulates calcitriol production, which boosts intestinal calcium (and phosphate) absorption, but the net renal phosphate loss outweighs the intestinal phosphate gain, so serum phosphate falls. The combined result is higher calcium and lower phosphate in the blood, which is why this option is correct. The other patterns don’t fit because PTH does not raise phosphate overall (it lowers it) and does not lower calcium (it raises calcium).

PTH raises serum calcium while lowering serum phosphate. It does this through coordinated actions on bone, kidney, and intestine. In bone, PTH stimulates osteoclast activity, releasing calcium and phosphate into the bloodstream. In the kidney, PTH increases calcium reabsorption in the distal tubule, and promotes phosphate excretion by reducing phosphate reabsorption in the proximal tubule. It also stimulates calcitriol production, which boosts intestinal calcium (and phosphate) absorption, but the net renal phosphate loss outweighs the intestinal phosphate gain, so serum phosphate falls. The combined result is higher calcium and lower phosphate in the blood, which is why this option is correct. The other patterns don’t fit because PTH does not raise phosphate overall (it lowers it) and does not lower calcium (it raises calcium).